The heat developable color light-sensitive materials are known in the field of art. For instance, methods for forming dye images by a coupling reaction of an oxidation product of a developing agent with a coupler are described, for example, in U.S. Pat. Nos. 3,761,270 and 4,021,240. Also, methods for forming positive color images by a light-sensitive silver dye bleach process are described, for example, in U.S. Pat. No. 4,235,957.
Further, a method has recently been proposed in which a diffusible dye is released or formed imagewise by heat development and the diffusible dye is transferred onto a dye fixing element. According to the method, either a negative dye image or a positive dye image can be obtained by changing the kind of dye providing compound used or the kind of silver halide used. More details thereof are described, for example, in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137 and 4,559,290, JP-A-58-149046 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-133449, JP-A-59-218443, JP-A-61-238056 and EP-A-210,660.
Many methods for obtaining positive color images upon heat development have been proposed. For instance, in U.S. Pat. No. 4,559,290, a method is described wherein an oxidized compound, which in its oxidized state does not have a dye releasing ability, obtained by converting a so-called DRR compound, is coexistent with a reducing agent (including a precursor thereof), the reducing agent is oxidized in correspondence to an exposure amount of silver halide upon heat development, and the oxidized compound is reduced with the remaining reducing agent which has been not oxidized, whereby a diffusible dye is released. Further, in U.S. Pat. No. 4,783,396 and Kokai Giho 87-6199 (Vol. 12, No. 22), a heat developable color light-sensitive material containing, as a compound capable of releasing a diffusible dye in a similar mechanism, a compound which can release a diffusible dye upon reductive cleavage of an N--X bond (wherein X represents an oxygen atom, a nitrogen atom or a sulfur atom) is described.
On the other hand, progress on computer graphics is remarkable in recent years as described, for example, in Eizojoho, edited by Kunigome Takeshi, October, 1993 published by Sangyo Kaihatsu Kiko Co., Ltd., and in order to output such image information, various systems of color printers (color hard copiers) of high image quality have been developed. For instance, printers for heat developable color light-sensitive materials using silver halide such as Pictrography 3000 and Pictrostat Digital 400 manufactured by Fuji Photo Film Co., Ltd. are commercially available.
Since negative-positive conversion is digitally conducted in these devices, conventional DRR compounds can be employed as they are in light-sensitive materials and images excellent in discrimination are available.
Although images having excellent image quality can be obtained in a short period of time using such light-sensitive materials, more rapid processing has been desired in a market place, recently. Processing at higher temperature is attempted in order to reduce the processing time. However, control of a period of time for processing is difficult under such a condition and unevenness of image occurs in some cases.
On the other hand, a technique for accelerating development by adding a reducing agent such as phenidone as an electron transfer agent is known for a long time. However, when such known reducing agents are used, problems, for example, degradation of stability of light-sensitive material, increase in density of white background area and decrease in color separation tend to occur.